Thousands of people in Alaska and British Columbia evacuated their homes to find higher ground or head inland as the tsunami sirens sounded, but the official warnings have since been lifted.

By Joe McDonough

Posted on January 24, 2018

Residents of Alaskan and Canadian coastal communities are breathing a sigh of relief today after potential tsunami devastation never eventuated.

A 7.9 magnitude earthquake hit the Gulf of Alaska, approximately 270km south of Kodiak Island, in the early hours of Tuesday, and the National Tsunami Centre was quick to issue an official warning.

Canada’s British Columbia was also in direct danger, and the entire US west coast and Hawaii was under a watch. They are all now in the clear.

But it was reportedly a tense few hours. In Kodiak and several settlements in British Columbia, the tsunami sirens sounded and thousands of people fleed their homes on the coast for higher ground or to head inland.

The emergency warning protocol and the swift response of authorities has since been lauded.

Tourist Alia Dharssi — who was staying in Tofino, Canada — was awoken by a call from reception at her accomodation at 2am and told of the terrifying threat.

“They told me there’s a tsunami warning, you have to go to the elementary school,” says Dharssi.

“I was glad they called because I couldn’t hear the sirens and I got up, left my room as quickly as I could, ran to the car and here I am.

“I was just thinking about those huge tsunamis you see in movies and then to come into town and see that people were calm and that there was a really clear evacuation plan and calmed me down a bit too.”

Why the tsunami threat didn’t eventuate

The International Tsunami Information Centre says the most destructive tsunamis are generated from earthquakes with a magnitude higher than 7.5 and that occur less than 70 kilometres deep, with an epicentre or fault line near or on the ocean floor.

Tuesday’s quake was recorded to have a magnitude of 7.9 and hit at a depth of just 25 kilometres in an area with quite a few fault lines — tick. But the type of earthquake was the key factor, according to CBC seismologist Johanna Wagstaffe.

If it had’ve occurred 90 kilometres to the west then it would have been a subduction earthquake and we could’ve seen a massive tsunami.

“This kind of earthquake was what is called a strike-slip earthquake,” Wagstaffe said. “That means there isn’t as much vertical displacement. So when you’re thinking of these rocks on the ocean floor, it didn’t punch up like some other earthquakes have.”

Instead of the water being displaced upward and forward in the case of a ‘megathrust’ quake, this water was moved much less by the horizontal motion, she explained.

“Where the Gulf of Alaska curves, you end up getting a splay of fault lines,” she continued. “There’s a really interesting section where this earthquake occurred where you can get all different kinds of motion happening.

“If it had’ve occurred 90 kilometres to the west then it would have been a subduction earthquake and we could’ve seen a massive tsunami.”

In 1964, that is exactly what took place. A 9.2 magnitude earthquake hit an area off the coast of Alaska at a depth of 25 kilometres, and being a megathrust rather than a strike-slip it produced a tsunami 30 metres high, killing more than 130 people.